The new cultivar of Prunus domestica of the present invention was created during 1987 in the course of prune breeding research carried out at the Kearney Agricultural Center of the University of California located at Parlier, Calif. Prunus domestica is commonly known as the European plum. The female parent (i.e., seed plant) was the European plum cultivar `Empress` (non-patented in the United States) and the male parent (i.e., pollen parent) was the prune cultivar `Primacotes` (non-patented in the United States). The parentage of the new cultivar is expressed as follows: EQU `Empress` .times.`Primacotes`.
During the course of the breeding program over 259 crosses were attempted following emasculation. Such cross-pollination made possible the harvest of 70 seeds at the end of the growing season. These were planted during 1988 and were given the group designation P88.16. The seedlings were grown in a nursery at Parlier, Calif. and were carefully studied during the remainder of 1988 and 1989. In the spring of 1990 these young nursery trees were transplanted into seedling rows. A single tree of the new cultivar of the present invention was selected during 1991 when such seedling fruited. This seedling initially was designated 3-6E-13.
It was found that the new Prunus domestica cultivar of the present invention:
(a) Exhibits a vigorous growth habit, PA1 (b) Demonstrates extreme precocity, PA1 (c) Forms flowers in abundance, and PA1 (d) Forms in abundance very large early maturing fruit that is dark purple under a greyish and waxy epidermal bloom that is particularly well suited for the fresh prune market.
The new cultivar has been asexually reproduced by grafting and budding. During the spring of 1992 the new cultivar was first asexually propagated at Parlier, Calif. by grafting onto two large six year old trees of `Marianna 2624` plum rootstock (non-patented in the United States). Subsequently the new cultivar additionally has been propagated on the same plum rootstock. `Myrobalan 29C` plum rootstock (non-patented in the United States), and `Nemaguard` peach rootstock (non-patented in the United States). The `Myrobalan 29C` rootstock is botanically classified as Prunus cerasifera and is a common rootstock used for prune trees in California. The new cultivar was found to reproduce true to form via such asexual propagation. All propagated trees were found to be very precocious with a small amount of fruit being produced as early as 1993 with a more substantial crop in 1994 and thereafter. Fruit is formed from buds on one-year old wood as well as an older spurs. The new cultivar was found to perform well on both plum rootstocks. On the `Nemaguard` peach rootstock a substantial outgrowth was found to occur at the graft union and the trees were distinctly smaller in size than when grown on the plum rootstock. Although no breakage has been observed at the union with the peach rootstock, propagation of the new cultivar on peach rootstock is not recommended. Since almost no topstock cultivars of Prunus are grown on their own roots in California, and many superior rootstocks are available, no effort has been made to grow the new cultivar of the present invention on its own roots.
The new cultivar has been further evaluated at test sites in the San Joaquin and Sacramento Valleys of California. These tests have further confirmed the commercial potential of the new cultivar.
In a typical year the fruit of new cultivar commonly reaches maturity during July at Parlier, Calif. This is nearly one month earlier at such location than that produced on the most commonly grown `Improved French` prune cultivar (non-patented in the United States). The generally oval-shaped fruit is considerably larger than that of the `Improved French` cultivar. Also, the fruit of the `Improved French` cultivar tends to be obovate often with a distinct neck and is of a lighter shade of purple than that of the new cultivar. In view of the abundant fruit set commonly achieved on the new cultivar it is recommended that the fruit be thinned on the tree to further enhance the quality of the fruit crop.
The new cultivar of the present invention is particularly well-suited for yielding an attractive and distinctive fresh market prune crop. Currently the fresh prune crop produced in the United States is largely exported to Pacific rim countries where it is held in particularly high regard. At the present time the `Moyer` cultivar (non-patented in the United States) is believed to be the most commonly grown and sold cultivar for the fresh market. The new cultivar can be readily distinguished from the `Moyer` cultivar by its larger fruit size and earlier fruit maturity.
Alternatively, the large fruit of the new cultivar can be dried. However, there are some disadvantages when the fruit is dried. The pit is large and is only semi-free from the flesh. Adequate drying times commonly exceed twenty hours and the fruit displays some tendency during drying to bleed, slab, and stick to the drying trays. The quality of the dried flesh is good, but because of such observations, utilization as a dried produce is less preferred.
The new cultivar of the present invention readily can be distinguished from its `Empress` plum parent in view of differences with respect to time of ripening, tree form, fruit soluble solids, and sensitivity to heat. The new cultivar commonly ripens in early July in the San Joaquin Valley of California, and the `Empress` cultivar commonly ripens in late August at the same location. The trees of the `Empress` cultivar tend to be very open and not highly branched. On the contrary, the new cultivar displays a well-branched tree that is capable of bearing heavy crops. The soluble solids level of the `Empress` cultivar commonly ranges from 12 to 15 degrees Brix at full maturity. This can be compared to 17 to 22 degrees Brix for the new cultivar at soft ripe maturity. The `Empress` cultivar is not grown commercially in the San Joaquin Valley of California because of its high sensitivity to fruit internal heat damage. On the contrary, the new cultivar can be grown to advantage in the hot interior California valleys.
The new cultivar of the present invention readily can be distinguished from its `Primacotes` prune parent in view of substantial differences with respect to fruit shape, fruit color, distribution on the tree, productivity, and sensitivity to heat. The fruit of the `Primacotes` cultivar is pyridiform-shaped with a broad but distinct neck and is reddish to reddish-purple in color when ripe. The fruit of the new cultivar is oval and possesses no neck, and when ripe is dark purple under a grey bloom. The fruit of the `Primacotes` cultivar is borne in large clusters on the end of the previous season's shoots with very little fruit being present on older shoots or spurs. On the contrary, the fruit of the new cultivar is borne throughout the tree both on the previous season's shoots as well as on the older hanger shoots and spurs. This leads to greater productivity for the new cultivar. The `Primacotes` cultivar when grown in the hot interior San Joaquin Valley of California, can show a moderate amount of fruit internal heat damage. On the contrary, the new cultivar at the same location is highly adapted and has never exhibited heat damage.
The new cultivar has been named `Tulare Giant`.